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is in decline. researchers at the australian institute of marine science say the reef has lost half of its coral cover over the past 27 years. there are multiple causes, including a destructive kind of starfish shown here. we look at what's behind it and what's at stake-- in australia and around the world-- with nancy knowlton, a coral reef biologist and a chair of marine science at the smithsonian national museum of natural history here in washington. welcome. >> thanks. how has all of this coral died off? do we know what's causing it? is it all that... >> it's not all the star fish. the star fish is about 42%. typhoons, big strong storms another 48% and then coral bleaching is the remaining 10% which is caused whenever the water gets too hot. >> ifill: so this is human causedded? >> yes. most of it is human caused. i mean a coral reef naturally goes through cycles of up and down. but it shouldn't be declining by half over course of 27 years. >> ifill: i feel like we have talked before about the declining coral cover. but not... but i'm wondering whether it's now picking up speed or whether thi
Search Results 0 to 6 of about 7 (some duplicates have been removed)